What is it like to sleep in space?

Pilot Michael L. Coats (left) and mission specialist Steven A. Hawley (right) fall asleep listening to music on the lower deck of the shuttle Discovery. What's it like for an astronaut to sleep in space? See more astronaut pictures.

What is it like to sleep in space?

When we settle into our beds at night, we usually experience a pleasant sense of unburdening. After a long day of walking, sitting, and standing, letting gravity do the work and sinking into a soft mattress can be a relief. But a little more than 200 miles (322 kilometers) above the Earth, astronauts live and work in zero gravity aboard the International Space Station (ISS), and going to sleep in zero gravity presents a much different situation.

The ISS is big -- it takes up about the same footprint as an American football field (including the end zones), and since launch now has more livable space than what you'd find in the average five-bedroom home, including two bathrooms, a gym (while in space, astronauts, on average, exercise for two hours every day in an effort to combat a side effect of life in space: bone and muscle loss), and a 360-degree bay window [source: NASA].

Since it docked in November 2000, the International Space Station has never been empty; in its first decade of operation more than 200 people visited the orbiting laboratory and spaceport, and it always has a permanent crew of six on board [source: NASA, Sample].

Crews on the ISS may live in space for long periods of time -- for example, Expedition 34 lived in space for 144 days -- and the details of each day they spend in space are scheduled beforehand. A typical weekday for the crew of Expedition 18 (the 18th permanent crew of the ISS), for instance, began with a 6 a.m. UTC (UTC is the same as GMT, which is used to reduce time zone confusion among countries) wake-up call, followed by 90 minutes of time for eating breakfast and getting ready for the day. By 7:30 a.m., the crew had conference calls with each country's control center, and embarked on a morning of science experiments, maintenance and small chores. Following an hour for lunch, the crew was back to work, along with more exercise much like the morning routine. With one final planning conference call with each control center, the day wrapped up around 5:30 or 6 p.m., followed by dinner at 8 p.m., and bedtime at 9:30 p.m. [source: Magnus].

After a busy day of exercising, research and maintenance work, the least an astronaut could ask for is a good night's sleep. But even the idea of "night" changes when you're in space, when an orbiter zooms around the Earth multiple times a day. And with the effects of microgravity and weightlessness, even the quality of sleep in space is different from that on Earth.

What's it like for astronauts to sleep in space? Do they just float around without anything to hold them down, or are they attached to something? Is it difficult to sleep in space, or do the effects of low gravity actually make it easier? To learn how astronauts get their Z's in zero gravity, read on.

How Astronauts Sleep in Space

Spacecraft like the International Space Station have pressurized cabins and are filled with the same kind of air we breathe on Earth, so the atmosphere on board is made to feel as close to sea level as possible. But microgravity causes astronauts to experience the effects of weightlessness, and setting up a mattress on the floor can't be part of the plan because not only would the astronaut float away after dozing off, the mattress itself would also drift off, creating the potential for midair collisions.

Because of this effect, astronauts could, theoretically, sleep almost anywhere in a spacecraft. Astronauts sleeping during space shuttle missions normally strap themselves into seats or attach sleeping bags to the walls; they'll avoid the cockpit since light from the sun can cause the area to heat up significantly and make slumber uncomfortable. Most of the crew on the ISS choose to sleep in their own cabin or in an ISS module -- American crew members' sleeping quarters are well-ventilated (to prevent breathing in the carbon dioxide you just breathed out), soundproof private cabin-for-one setups where an astronaut can not only catch some Z's but also catch up on e-mail. The catch is that they need to tether themselves to something to avoid floating away in the air currents. Most astronauts choose to sleep as closely to how they would on Earth, in sleeping bags tethered to the floor, the walls, or the ceiling. In the microgravity environment there is no such thing as "up," which means it's just as easy to sleep vertically as you would horizontally back home. It's also important to secure your arms (and legs) to avoid them hovering as you sleep.

Adjusting to sleep in space takes a long time for astronauts. Our bodies and brains are used to certain circadian rhythms -- the 24-hour cycle of waking and sleeping -- and disturbing them can cause sleep difficulties.

Waking Up With the Sound of Music

Ground operations broadcast songs into the space shuttle cabin as wake-up calls for sleepy astronauts; song selections have included "Danger Zone" by Kenny Loggins from "Top Gun" and "Con Te Partiro" sung by Andrea Bocelli. Crew members on the ISS, though, rely on regular alarm clocks.

John Glenn tries on a harness meant to monitor body functions while sleeping in space.

The Difficulties of Sleeping in Space

How long you sleep and how well you sleep are important to your mood, how well you concentrate and how much energy you have, as well as how healthy your body is; chronic sleep deprivation can lead not only to irritability but also to attention deficit and an increased risk of cardiovascular disease, diabetes, hypertension, and obesity [source: American Academy of Sleep Medicine].

Despite pre-mission training and preparation living on board a space station can be disorienting for the body. To avoid any distracting light and heat from the sun, for example, astronauts will cover up any windows they may be near. Astronauts can also choose to wear black sleep masks, the same kind that some people wear on Earth when they want to shut out distracting light. On top of excessive light, strange noises are a big part of the ISS. Because fans, air filters and other noisy equipment provide life support to the astronauts, the ISS is often filled with constant whirring noises -- a constant hum. Astronauts sometimes sleep with earplugs to dampen the sound, but after a while many report they simply get used to it.

Combine the light and the noise with the unnatural feeling of floating, motion sickness, aches and pains, poor ventilation and temperature control, as well as a new sunrise every 90 minutes (the amount of time it takes the space station to circumnavigate the Earth) insomnia and sleep deprivation are a common and serious problem for humans in space; NASA reports that sleeping pills are the second most common drug astronauts take (painkillers are the most common). To help combat astronaut insomnia NASA also budgets at least 8 hours of sleep every day, promotes relaxation techniques, and provides sleep hygiene education but despite it all astronauts average between 30 to 60 minutes less sleep each night than they got at home on Earth [source: Worth]. NASA has also invested $11.4 million to update the fluorescent lights in the ISS's U.S. Orbital Segment with bulbs designed to exploit that our bodily clocks are wound by exposure to light [source: Worth].

And yes, in case you were wondering, it is possible to snore in space.

Lots More Information

Author's Note: What is it like to sleep in space?

I like when I get to write about NASA; NASA research has changed the way we live in our daily lives, with inventions from shoe insoles and scratch-resistant lenses to ear thermometers and water filters. They've also given us memory foam. That's the temper foam found in Tempurpedic (and similar) mattresses, which seems ironic considering sleep deprivation and insomnia are big problems for astronauts living in space.

Something like 9 million Americans rely on prescription sleep-inducing meds to get a decent night's sleep, and that's not even counting those of us who try teas, over-the-counter remedies, or just suffer through it. The next time you can't get comfortable in your bed and find yourself thinking that surely an anti-gravity pod would be more comfortable than your mattress, think again -- insomnia plagues humans in space, too.

Canright, Shelley. "Teaching From Space: A Day in the Life Aboard the International Space Station - Exercising in Space." National Aeronautics and Space Administration (NASA). June 4, 2013. (Aug. 25, 2013) http://www.nasa.gov/audience/foreducators/teachingfromspace/dayinthelife/exercise-adil-index.html

Halvorson, John. "Zvezda, the new crew quarters for the International Space Station will rank right up there with the penthouse at the Ritz." Space.com. July 5, 2000. http://www.space.com/news/spacestation/zvezda_life_000705.html